Catheters are placed at various locations within a patient for a wide variety of purposes and medical procedures. For example only, one type of catheter is a balloon dilatation catheter which is used in the treatment of a vascular stenosis. Such a catheter has a balloon at its distal end which is intended to be placed, in a deflated condition, within the stenosis, and then inflated while in the stenosis to expand radially the stenosed lumen of the blood vessel. Typically, the placement of such catheters involves the use of a guidewire which may be advanced through the patient's vasculature to the location which is to be treated. The catheter, which has a guidewire lumen adapted to receive the guidewire, then is advanced over the wire to the stenosis, or, alternatively, the wire and catheter may be advanced in unison to the stenosis with the wire protruding from the distal end of the catheter.
Essentially, there are three types of catheters: "over-the-wire" catheters, "monorail" catheters and "fixed balloon on a wire" catheters.
An over-the-wire catheter comprises a guidewire lumen which extends the entire length of the catheter. The guidewire is disposed entirely within the catheter except for the distal and proximal portions of the guidewire which extend beyond the distal and proximal ends of the catheter respectively. A typical over-the-wire balloon dilatation catheter is disclosed in Simpson et al. U.S. Pat. No. 4,323,071.
Over-the-wire catheters have many advantages traceable to the presence of a full-length guidewire lumen such as good stiffness and pushability for readily advancing the catheter through the tortuous vasculature to the stenosis, and the availability of the guidewire lumen for transporting radiocontrast dye to the stenosis or for pressure measurements.
However, over-the-wire catheters do suffer some shortcomings. For example, it often becomes necessary, in the performance of a catheter procedure, to exchange the indwelling catheter for another catheter having a different size balloon. In order to maintain a guidewire in position while withdrawing the catheter, the guidewire must be gripped at its proximal end to prevent it from being pulled out of the blood vessel with the catheter. However, the catheter, which may typically be on the order of 135 centimeters long, is longer than the proximal portion of the standard guidewire which protrudes out of patient. For this reason, in order to effectuate an exchange of an over-the-wire catheter, a wire of the order of 300 centimeters long is necessary.
In one type of over-the-wire catheter exchange, the guidewire first is removed from the lumen of the indwelling catheter. Then a longer exchange wire is passed through the catheter to replace the original wire. Then, while holding the exchange wire by its proximal end to maintain it in place, the catheter is withdrawn proximally from the blood vessel over the exchange wire. After the first catheter has been removed, the next catheter is then threaded onto the proximal end of the exchange wire and is advanced along the exchange wire and through the patient's blood vessels until the distal end of the catheter is located as desired. The exchange wire may be permitted to remain in place or may be exchanged for a shorter, conventional length guidewire. Alternatively, the length of the initial guidewire may be extended by way of a guidewire extension apparatus (see Gambale et al. U.S. Pat. No. 4,917,103).
However, with either exchange process, the long length of the exchange wire dictates that two operators are needed to perform the procedure. During the procedure, it is necessary that the operators communicate with each other which makes the procedure time consuming. Furthermore, the long length of the exchange wire renders it awkward to handle.
These shortcomings of the over-the-wire catheters led to the development of the monorail type catheter. Catheters of this type, which are described in U.S. Pat. Nos. B1 4,762,129, 5,040,548 and 5,061,273, are formed so that the guidewire is located outside of the catheter except for a short segment at the distal end of the catheter, which passes over the wire. The distal segment of the catheter has a short lumen which extends from the distal tip of the catheter to a more proximally located opening near the distal tip. In use, the guidewire is placed initially in the patient's vascular system. The distal segment of the catheter then is threaded onto the wire. The catheter can be advanced alongside the wire with its distal segment being attached to and guided along the wire. The catheter can be removed and exchanged for another catheter without the use of the usual double length exchange wire and without requiring withdrawal of the initially placed guidewire.
Although such a monorail catheter system may avoid the requirement for using a long exchange wire, it presents several difficulties. For example, it is not possible to exchange guidewires in an indwelling catheter as can be done with over-the-wire catheters. Additionally, the device presents a potential for damaging the delicate inner surface of an artery from a tension load applied to the guidewire which would tend to straighten the artery. Also, there is an increased risk of guidewire entanglement in those procedures where multiple guidewires are used, because the guidewires are exposed within the blood vessel.
The monorail catheters, which do not include a guidewire lumen for the entire length of the catheter, also lack the desired stiffness and pushability for readily advancing the catheter through tortuous blood vessels. In addition, the lack of a full length guide-wire lumen deprives the physician of an additional lumen that may be used for other purposes, e.g., pressure measurement and distal dye injection.
There is, therefore, a need for a new and improved catheter apparatus which incorporates the benefits of both the over-the-wire and the monorail catheters but without their attendant drawbacks.
In general, it is an object of the present invention to provide a catheter apparatus which facilitates both the rapid exchanges of the indwelling catheter without the use of an extension wire while providing sufficient stiffness and pushability to readily advance the catheter apparatus through the tortuous vasculature.